The present invention relates to an installation for exposing a double-sided printed circuit card to light.
Amongst the operations required in making a printed circuit card, there is a step of insolation, in particular for defining the conductor tracks of the printed circuit by photoetching. The function of the corresponding installation is to take the printed circuits covered in a film or in a photosensitive resist and to expose them to ultraviolet light for a given length of time through an artwork so as to insolate the corresponding portion of the photosensitive film or resist.
The installation in question is of the type in which the printed circuit is a double-sided printed circuit, i.e. conductive tracks need to be made on both faces of the insulating medium of the printed circuit card, with both faces being made simultaneously.
Consequently, in such an installation, there is a top artwork support and a bottom artwork support, and the card whose two faces are to be insolated is placed between them. To enable the card for insolation to be put into place, it is necessary to be able to move the top artwork support away from the bottom support. These artwork supports are mounted on frames, and the top support is thus associated with a top frame which must be driven with up and down motion.
Such installations are described in particular in European patent applications EP 0 618 505 and EP 0 807 855 in the name of the Applicant.
When the top artwork frame reaches its bottom position, it is accurately positioned relative to the bottom frame by the presence of male and female centering cones. It is necessary for this operation to be repeatable with high accuracy, to within about 5 microns.
When the printed circuit cards to be made, i.e. to be insolated on both faces, are of relatively small dimensions, then it is relatively easy to achieve co-operation between the male and female cones of the moving top frame and of the stationary bottom frame. However, with printed circuit cards of greater dimensions, it is necessary to provide a machine which is itself of greater dimensions and which has a top frame of much greater dimensions and consequently of much greater weight, e.g. 250 kg, in order to obtain stiffness matching the precision of the installation. Under such circumstances, while the top frame is being lowered relative to the bottom frame, co-operation between the male and female cones of the top frame and of the bottom frame gives rise to a certain number of difficulties, in particular due to problems of friction between the male and female cones.
An object of the present invention is to provide an installation for exposing a double-sided printed circuit card to light through artworks, in which the co-operation between the male and female cones of the top frame carrying the top artwork and the bottom frame can be obtained easily in spite of the considerable weight of the moving top frame.
According to the invention, this is achieved by an installation for exposing a double-sided printed circuit card to light through artworks, the installation comprising a structure, a first artwork-support frame fixed relative to the structure, a second artwork-support frame movable relative to the structure, vertical displacement means for displacing said second. frame between a waiting position and a working position in which the two frames are close to each other, and mechanical link means between the displacement means and said second frame, the first and second frames having relative positioning members suitable for mutual co-operation when the two frames are in the working position,
the installation being characterized in that the mechanical connection means comprise:
first means forming a first horizontal connection surface mechanically connected to the vertical displacement means;
means forming a second horizontal connection surface secured to said second frame;
support means for providing substantially frictionless co-operation in a horizontal plane between said first and second connection surfaces, thereby enabling said second frame to move horizontally relative to the structure; and
controllable locking means for temporarily locking said first and second support surfaces together.
It will be understood that by connecting the frame in this way to the means for displacing the frame vertically, it is possible to obtain co-operation between the male and female positioning cones without giving rise to high stresses. However, outside the final stage of co-operation between the cones, the controllable locking means serve to ensure a rigid connection between the displacement means and the frame of the top artwork support.
Preferably, pneumatic means controllable in vertical displacement are interposed between the frictionless co-operation means and the displacement means in order to drive vertical relative displacement between the top frame and the vertical displacement means. This disposition makes it possible to xe2x80x9clightenxe2x80x9d or reduce the apparent weight of the top frame carrying the top artwork support so as to provide a safety function for the personnel using the machine. It is recalled that the top frame assembly can weigh about 250 kg. This disposition also makes it possible to lighten the top frame at the moment when it comes into contact with the bottom frame. It is thus possible to limit the stresses applied to the bottom frame while this contact is being made. Nevertheless, when the top frame comes into contact with the bottom frame, it is necessary for the apparent weight of the frame to be sufficient to overcome the force developed by the inflatable gasket which is provided on the bottom frame so as to be able to evacuate between the two frames.
Also preferably, the substantially frictionless co-operation means comprise balls which are interposed between the first and second horizontal connection surfaces.